ES2971472T3 - Method of manufacturing a cemented carbide or cermet body - Google Patents

Abstract

A method for manufacturing a cemented carbide and/or cermet comprising the steps of: a) providing a powder comprising metal carbide and binder metal and optionally metal nitride(s); b) mixing the powder composition under vacuum; c) adding at least one organic binder to the powder composition; d) mixing at least one organic binder with the powder composition under vacuum and raising the temperature to a predetermined temperature and maintaining the temperature for a predetermined time until the organic binder has melted; e) subjecting the mixture obtained from step d) to shaping and sintering processes; wherein one or more dispersing agents are added to the powder composition in step a). (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Method of manufacturing a cemented carbide or cermet body

Technical field

The present invention relates to a new method of manufacturing a cemented carbide and/or a cermet in which the cemented carbide and/or the cermet has a microstructure with improved homogeneity.

Background of the invention

Cemented carbide or cermet is commonly used for rotating or cutting tools as it has good wear properties.

To achieve optimal properties, the microstructure should contain as few conglomerates or clusters of enlarged carbide grains as possible, as well as as few binder gaps as possible and, furthermore, as little porosity as possible. Patent document EP 1724363 A1 describes the wet grinding of a powder mixture containing hard constituent powders based on carbides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and more than 15 % by weight of Co and/or Ni binder phase powders, as well as pressing and spray drying agents. 0.05-0.50% by weight of a complex-forming and/or pH-increasing/decreasing additive, such as triethanolamine, hydroxides or acids, and a thickener are added to the powder mixture before grinding. amount of 0.01-0.10% by weight.

Patent document US5922978 A describes a pressable powder formed by a method comprising mixing, in essentially deoxygenated water, a first powder selected from the group consisting of a transition metal carbide and a transition metal with an additional component selected in the group consisting of a second powder composed of a transition metal carbide, a transition metal or mixtures thereof; an organic binder and a combination thereof and drying the mixed mixture to form the pressable powder, wherein the second powder is chemically different from the first powder. The pressable powder can then be formed into a formed part and subsequently densified into a densified part, such as a cemented tungsten carbide, and triethanolamine could be added as a corrosion inhibitor.

Patent document US6878182 B2 describes a suspension based on ethanol-water and containing metal carbide and metallic raw materials as well as stearic acid and a low concentration of polyethyleneimine (PEI). The concentration of PEI is 0.01 to 1% by weight with respect to the weight of the raw material.

Patent document EP1153652 A1 describes a process for mixing WC and Co with additional constituents suitable for manufacturing cemented carbides, with water, ethanol or mixtures of ethanol and water, and a polyethyleneimine-based dispersant to achieve a well-dispersed suspension suitable for spray drying. The method is characterized by adding to the suspension as a dispersant between 0.1 and 10% by weight, preferably between 0.1 and 1% by weight, of a polyethyleneimine-based polyelectrolyte.

US Patent Document 4,478,888 is directed to a process for producing a mixture of carbide quality powder for manufacturing a cemented metal carbide, wherein in this process a mixture of metal carbide particles and wax is formed at a temperature above the melting point of wax.

Patent document JP 2012052237 A describes a method of producing a cemented carbide that has high transverse strength with less variation, and a cemented carbide rotary tool that has excellent breakage resistance even when used for small diameter drilling. or high feed cutting.

Patent document EP 2647731 A1 describes a method for producing a cemented carbide, in which acoustic waves are used to achieve a homogeneous mixing of a powder mixture.

Patent document EP 0471 123 A1 is directed to a process for preparing an inorganic article by mixing an inorganic powder, water and a dispersant in a suspension, heating the mixture, in turn mixing the heated mixture with a thermally gelable polymeric binder. a temperature above the gelling point of the polymer to form a slurry mixture and cool the mixture before extruding articles by extruding the mixture.

Patent document US 5,619,000 describes a method for producing a sintered body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgy methods of grinding, pressing and sintering of powders.

Patent document CN 101892409 A is directed to a method for preparing a hard coating alloy for grinding. The method comprises the following steps: adding a metallic cobalt powder and a tantalum carbide powder to a tantalum carbide powder whose particle size is between 4 and 6 pm and the amount of total carbon is between 6.08 and 6 .13 percent to prepare a mixture; perform compression molding and vacuum sintering of the mixture to prepare a high intensity and high toughness hard alloy substrate consisting of 10 to 13 weight percent cobalt metal powder, 1 to 3 weight percent cobalt metal powder tantalum carbide and 84 to 89 weight percent tungsten carbide powder; and carry out innovative grinding and rounding machining treatment of the hard alloy substrate and carry out super nitrogen-titanium-aluminum-nitrogen physical vapor deposition (PVD) coating treatment

In all of the above-mentioned descriptions except the last, dispersing agents, such as triethanolamine and/or polyethyleneimine, are added to a wet mixture or suspension. The problems with these methods are that the mixing of the different constituents will be incomplete and therefore the products obtained will not have the desired homogeneous microstructure when sintered and therefore will not have the desired properties. The present invention will solve or at least reduce the problems mentioned above.

Summary

In one aspect, the present invention describes a method for manufacturing a cemented carbide and/or a cermet comprising the steps of:

a) providing a powder comprising metal carbide(s) and binder metal(s) and optionally metal nitride(s);

b) mix the powder composition provided in step a) under vacuum before

c) adding at least one organic binder to the powder composition;

d) mixing the at least one organic binder with the powder composition under vacuum and raising the temperature to a predetermined temperature and maintaining the temperature for a predetermined time until the organic binder has melted;

e) subjecting the mixture obtained in step d) to shaping and sintering processes;

wherein one or more dispersing agents are added to the powder composition in step a) and wherein one or more cooling agents are added to the powder composition in step b).

Therefore, at least one dispersing agent is added to the dry powder mixture in the first stage.

In another aspect of the present description, which is not part of the invention, a body of cemented carbide or cermet is obtained according to the method defined above or below, in which the microstructure of the cemented carbide or cermet does not have conglomerates. of carbide grains with a diameter > 5 x the average carbide grain size.

In another aspect, which is not part of the invention, a body of cemented carbide or a cermet is obtained according to the method defined herein above or hereinafter, body of cemented carbide or cermet that is used for a rotary cutter or any other application of wear.

The method described above or hereinafter will provide a desired homogeneous powder mixture which in turn will result in a product (cemented carbide and/or cermet) with a more homogeneous microstructure and therefore with improved properties, for example, higher strength tensile, greater hardness, greater toughness against fracture and/or greater resistance to wear. Consequently, this will result in improved performance when cemented carbide and/or cermet is used for a rotary cutter or wear part.Brief Description of Drawings.

Figure 1: describes an optical micrograph showing the microstructure of the cemented carbide from test 1 and showing an example of a hard metal conglomerate.

Figure 2: depicts an optical micrograph showing the microstructure of the cemented carbide from test 1 and showing an example of binding gaps.

Figure 3: Describes an optical micrograph showing the microstructure of the cemented carbide from test 3 Figure 4: Describes an optical micrograph showing the microstructure of the cemented carbide from test 8 All optical micrographs were taken with an Olymus PMG3-LSH-3 inverted microscope .

Detailed description

The present invention describes a method for manufacturing a cemented carbide and/or a cermet that comprises the steps of:

a) providing a powder comprising metal carbide(s) and binder metal(s) and optionally metal nitride(s);

b) mixing the powder composition under vacuum;

c) adding at least one organic binder to the powder composition;

d) mixing the at least one organic binder with the powder composition under vacuum and raising the temperature to a predetermined temperature and maintaining the temperature for a predetermined time until the organic binder has melted;

subjecting the mixture obtained in step d) to shaping and sintering processes; wherein one or more dispersing agents are added to the powder composition in step a) and wherein one or more cooling agents are added to the powder composition in step b).

The method, in an aspect that is not part of the invention, preferably comprises preparing a dough for use in extrusion. In such case, the method preferably comprises adding organic solvents (monopropylene glycol (MPG) and/or oleic acid) to the mixture obtained to lubricate the mixture before sintering in step e) above.

Furthermore, according to the present method, the one or more dispersing agents are selected from triethanolamine (TEA) or polyethyleneimine (PEI) or a mixture thereof.

Furthermore, according to the present method as defined above or below, the powder provided in step a) comprises metal carbide(s) and binder metal(s) and metal nitride(s). .

When the at least one organic binder is added to the cemented carbide or cermet production process, a two-step mixing process is necessary. This is because if the metal carbide powder, metal nitride powder, metal binder powder and organic binders are mixed together in one step, the organic binder will adhere to the metal binder powder, preventing efficient mixing. and, consequently, will provide a cemented carbide or cermet with a non-homogeneous microstructure. The desired homogeneity of the microstructure of the cemented carbide or cermet is obtained by adding one or more dispersing agents to the powder composition, thus ensuring that the composition is well mixed before adding at least one organic binder. The present invention provides an effective method for obtaining cemented carbides and/or cermets that have a homogeneous mixture as one or more dispersing agents are added to the first mixing stage (stage a), in which powders of metal carbide(s) and metabinder(s) and optionally metal nitride(s). Therefore, this mixing step is a dry mixing step having a moisture content less than or equal to 5% by weight (relative to the total powder composition). The mixing step is defined as dry because no significant amounts of water and/or ethanol and/or any other solvent are added to produce a wet suspension. The only liquid added in this step is, if necessary, a small amount of liquid in the form of a cooling agent. The cooling agent is selected from water, ethanol and any other suitable solvent that would evaporate easily under the mixing conditions. The temperature in this first mixing step should be kept below 50°C to avoid oxidation. The powder composition must be kept as dry as possible during this first mixing stage, therefore the moisture content is less than or equal to 5% by weight. No cooling agent is added until the temperature begins to rise above 50°C and when the temperature begins to rise the amount of cooling agent added should be as little as possible to keep the powder mixture as dry as possible, i.e. , with a moisture content less than or equal to 5% by weight. During this step, the one or more dispersing agents are added. The addition of one or more dispersing agents at this stage ensures that the metal carbide(s) and metal binder(s) powders and optionally metal nitride(s) are mixed well before adding to the minus an organic binder in the second mixing stage.

The agent (one) or more dispersing agents is selected from triethanolamine (TEA), polyethyleneimine (PEI) or a mixture thereof. The amount of dispersing agent is 0.05 - 0.5% by weight with respect to the total powder mixture.

According to the present method, the cemented carbide comprises metal carbide(s) and/or metal nitride(s) in the range of 70 to 97% by weight and binder metal(s) in the range from 3% by weight to 30% by weight (% by weight is relative to the total cemented carbide content). The metal carbide(s) and/or the metal nitride(s) comprise(s) more than or equal to 70% by weight of tungsten carbide and less than or equal to 30% by weight of at least another metal carbide and/or metal nitride selected from titanium carbide, titanium nitride, tantalum carbide, tantalum nitride, niobium carbide and a mixture thereof (the % by weight is with respect to the total content of metal carbides and metal nitrides).

According to the present method, the cermet comprises metal carbide(s) and/or metal nitride(s) in the range of 70 to 97% by weight and binder metal in the range of 3% by weight to 30 % by weight (the % is with respect to the total content of the cermet). Furthermore, the cermet comprises a combination of one or more metal carbides and/or metal nitrides selected from titanium carbide, titanium nitride, tungsten carbide, tantalum carbide, niobium carbide, vanadium carbide, molybdenum carbide, chromium and a mixture thereof, with the highest proportion based on titanium, that is, the titanium is in the form of carbide and/or nitride and is in the range of 30 to 60% by weight (% by weight is regarding the total cermet content). Furthermore, the cermet does not comprise any free hexagonal tungsten carbide. The cermet comprises tungsten carbide without any free hexagonal structure in the range of 10 to 20% by weight. Hexagonal tungsten carbide has a structure made up of a simple hexagonal lattice of tungsten atoms placed directly on top of each other with the carbon atoms filling half of the interstices, giving both tungsten and carbon a regular trigonal prismatic structure.

The cermet and/or cemented carbide may also comprise small amounts, such as less than or equal to 3% by weight, of other compounds, for example, MoC, VC and/or C<3>C<2>.

According to one aspect of the invention, the binder metal(s) are selected from cobalt, molybdenum, iron, chromium or nickel and a mixture thereof.

According to the method defined above or below, one or more organic solvents are optionally added in step d).

The method as defined herein above or below, optionally comprises that the mixture obtained in step d) is dried after shaping and before sintering in step e).

According to another aspect of the invention, the shaping is carried out by extrusion, pressing operation or injection molding.

In the first mixing stage, the metal carbide(s) and/or the metal nitride(s) can be selected from the group including tungsten carbide, tantalum carbide, niobium carbide, titanium carbide, titanium nitride, tantalum nitride, vanadium carbide, molybdenum carbide, chromium carbide and mixtures thereof. The binder metal is any of a single binder metal or a mixture of two or more metals or an alloy of two or more metals and the binder metal is selected from cobalt, molybdenum, iron, chromium or nickel. However, which carbides and/or nitrides are selected and their proportions depend on whether the final product will be a cemented carbide or a cermet and the desired end properties of the final product.

Once the components from the first mixing step are well mixed, one or more organic binders are added. The at least one organic binder used in the process as defined above or hereinafter is selected from polyethylene glycol (PEG), methyl cellulose (MC), wax systems such as petroleum wax, vegetable wax or synthetic wax, polyvinyl butyral (PVB) , polyvinyl alcohol (PVA) and a mixture thereof. The organic binder could also be a mixture of the same organic binder but of different types, for example a mixture of different PVA, PEG or MC.

In this second step, the mixing process continues under vacuum (to avoid air trapped in the mixture) until the temperature reaches approximately 70 °C (or higher depending on the organic binder) to ensure that the organic binders have melted or are completely scattered. If a mass is to be produced, for example if cemented carbide or cermet is to be formed using an extrusion process, then additional wet organic solvents such as oleic acid, monopropylene glycol or water can also be added in the second mixing stage. In this case, an additional drying step would be necessary after forming and before sintering.

According to the present method, mixing can be carried out using a planetary mixer. A planetary mixer contains blades that rotate on their own axes and at the same time on a common axis, providing complete mixing in a short period of time. The advantage of this type of mixer is that, compared to the conventional ball mill commonly used to mix powders to be used to obtain cemented carbides and cermets, the mixing time is reduced and there is no wear or erosion of the raw materials. Other high speed mixing devices could also be used, for example a high speed rotor.

In one aspect, which is not part of the invention, the cemented carbide or cermet obtained has a microstructure without conglomerates of metal grains with a diameter > 5 x the average grain size of hard metal. According to the method defined above or below, the cemented carbide and/or cermet thus obtained has a microstructure that does not comprise conglomerates of enlarged carbide grains with a diameter greater than 5 x the average carbide grain size. and not greater than 0.5 cm per cm2. The average grain size of carbide is determined by the linear intersection method according to ISO 4499. A cluster is defined as 5 or more grains located side by side. An example is shown in Figure 1.

In another aspect, which is not part of the invention, the cemented carbide or cermet microstructure does not have binder gaps with a diameter > 5 x the average hard metal grain size. Furthermore, according to the method defined above or below, the cemented carbide and/or cermet thus obtained has a microstructure that does not comprise binder gaps with a diameter greater than 5 x the average grain size of carbide and no more than 0 .5 cm by cm.2. A binder gap is defined as an area consisting solely of binder with no carbide grains in that region. An example is shown in Figure 2.

In another aspect, which is not part of the invention, the microstructure of the cemented carbide or cermet has a type A porosity of A00 or A02. Furthermore, according to the method defined above or hereinafter, the cemented carbide and/or cermet body thus obtained has a microstructure with an A-type porosity of A00 or A02. Porosity is measured according to ISO 4505. The type of porosity is defined as voids less than 10 pm in diameter. A00 corresponds to the total absence of any pore volume and A02 means a maximum volume of type A pores of 0.02% of the total volume of the material.

In another aspect, which is not part of the invention, the cemented carbide or cermet can be used for a rotary cutter or any other wear application. The cemented carbide or cermet body obtained by the method defined above or hereinafter can be used to manufacture a rotary cutter or any other wear object, for example, mining drill bits or drum drilling tools.

The present invention is best illustrated by the following non-limiting examples.

Examples

Table 1 describes the different compositions used to mix WC-Co cemented carbide. For all these tests, mixing was carried out in two steps using an Eirich mixer, model RO2VAC. First, tungsten carbide (WC), cobalt (Co), chromium carbide (C<3>C<2>) and carbon (C) powders were mixed. In trials 3 to 12, TEA and/or PEI were also added in this step. The constituents were mixed by running the rotor at 270 rpm while vacuum was applied and then the first mixing step was performed for 20 min at 4500 rpm. Distilled water was added in a minimum amount to maintain a temperature of 50°C when the powder temperature began to rise.

In the second mixing stage, the dry organic constituents (PEG) were added and mixed at 1500 rpm under vacuum until the temperature reached approximately 70 °C and all of the PEG had melted; this took approximately 3 minutes. For trials 1 and 2, TEA was also added in this step. Afterwards, the organic solvents, oleic acid and/or monopropylene glycol (MPG), were also added and mixing continued so that a mass was formed. The mixer was turned off when the rotor speed decreased due to the viscosity of the material.

Samples were taken from tests 1 to 12 before the addition of the organic binders. A small amount of PEG 300 was added and the samples were pressed to form 8x7x24 mm compacts and then sintered at 1450°C at 50 bar pressure. The sintered samples were mounted in resin and polished with sand of grain size 180 and then 220 pm. The porosity of the samples was examined under an optical microscope and evaluated according to the ISO 4505 standard.

As can be seen in Table 1, type A porosity was significantly reduced in tests 3-12, in which the dispersing agent was added in the first mixing step compared to tests 1 and 2, where the dispersing agent was added in the second mixing step.

The samples were then etched using Murakami reagent for 4 min and then examined again under an optical microscope to evaluate the homogeneity of the microstructure. Tests 1 and 2 produced cemented carbide bodies with microstructures containing large agglomerates of enlarged carbide grains and large binder gaps. For example, Figures 1 and 2 show the microstructure of the cemented carbide body produced from test 1. Figure 1 shows an agglomerate of grains having a grain size diameter greater than 5 times the average grain size of the metal. hard. The chipboard measures approximately 14 pm wide at the widest section. Figure 2 shows binder gaps in the sample, one with a diameter of approximately 3.4 pm and the other with a diameter of approximately 4.1 pm, both greatly exceeding a diameter of 5 x the average grain size of heavy metal.

Figures 3 and 4 show examples of the microstructure of cemented carbide bodies from tests 3 and 8 respectively. It can be seen that the microstructures have good grain size uniformity, without conglomerates of enlarged carbide grains or binder gaps.

Claims (9)

1. A method for manufacturing a cemented carbide and/or a cermet comprising the steps of: a) providing a powder comprising metal carbide(s) and binder metal(s) and optionally metal nitride(s); b) mixing the powder composition provided in step a) under vacuum before c) adding at least one organic binder to the powder composition; d) mixing the (at least one) organic binder with the powder composition under vacuum and raising the temperature to a predetermined temperature and maintaining the temperature for a predetermined time until the organic binder has melted; e) subjecting the mixture obtained in step d) to shaping and sintering processes; wherein one or more dispersing agents are added to the powder composition in step a) and wherein one or more cooling agents are added to the powder composition in step b). 2. The method according to claim 1, wherein the cemented carbide comprises more than or equal to 70% by weight of tungsten carbide and not more than or equal to 30% by weight of at least one other metal carbide and/or nitride metal selected from titanium carbide, tantalum carbide, tantalum nitride, titanium nitride, niobium carbide, vanadium carbide, molybdenum carbide, chromium carbide and mixtures thereof. 3. The method according to claim 1, wherein the cermet comprises titanium carbide, titanium nitride, tungsten carbide, tantalum carbide, tantalum nitride, niobium carbide, vanadium carbide, molybdenum carbide, chromium carbide and a mixture thereof. 4. The method according to any of the preceding claims, wherein said binder metal or metals are selected from cobalt, molybdenum, iron, chromium or nickel and a mixture thereof. 5. The method according to any of the preceding claims, wherein the mixing is carried out using a planetary mixer. 6. The method according to any of the preceding claims, wherein one or more organic solvents are added in step d). 7. The method according to any of the preceding claims, wherein the mixture obtained in step d) is dried after shaping and before sintering in step e). 8. The method according to any of the preceding claims, wherein the one or more dispersing agents are selected from triethanolamine (TEA) or polyethyleneimine (PEI) and a mixture thereof. 9. The method according to any of the preceding claims, wherein the shaping is carried out by extrusion, pressing operation or injection molding.